"Experiments on Plant Hybridization" is a seminal paper written in 1865 and published in 1866[1] [2] by Gregor Mendel, an Augustinian friar considered to be the founder of modern genetics. The paper was the result after years spent studying genetic traits in Pisum sativum, the pea plant.
In his paper, Mendel compared 7 pairs of discrete traits found in a pea plant:
| Characteristics | Contrasting traits | Offspring traits | |
|---|---|---|---|
| Flower Color | Violet and White | Violet | |
| Flower Position | Axial and Terminal | Axial | |
| Plant Height | Tall and Dwarf | Tall | |
| Seed Texture | Round and Wrinkled | Round | |
| Seed Color | Green and Yellow | Yellow | |
| Pea Pod Texture | Inflated and Constricted | Inflated | |
| Pea Pod Color | Green and Yellow | Green |
Through experimentation, Mendel discovered that one inheritable trait would invariably be dominant to its recessive alternative. Mendel laid out the genetic model later known as Mendelian inheritance or Mendelian genetics. This model provided an alternative to blending inheritance, which was the prevailing theory at the time.
Mendel read his paper to the Natural History Society of Brünn. It was published in the Proceedings of the Natural History Society of Brünn the following year.
Mendel's work received little attention from the scientific community and was largely forgotten. It was not until the early 20th century that Mendel's work was rediscovered and his ideas used to help form the modern synthesis.
In 1936, the statistician Ronald Fisher used a Pearson's chi-squared test to analyze Mendel's data and concluded that Mendel's results with the predicted ratios were far too perfect, suggesting that adjustments (intentional or unconscious) had been made to the data to make the observations fit the hypothesis.[3]
Later authors have suggested Fisher's analysis was flawed, proposing various statistical and botanical explanations for Mendel's numbers.[4] It is also possible that Mendel's results are "too good" merely because he reported the best subset of his data - Mendel mentioned in his paper that the data were from a subset of his experiments.
Modern geneticists have inferred the 7 genes studied by Mendel. It is impossible to know for certain, but the identification is possible to a high degree of confidence based on Mendel's description, and the pea varieties grown in central Europe in the 1850s.[5] The table shows that the 7 genes appeared on 5 chromosomes. Of these, the only pair with significant linkage are V and LE, who are 12.6 map units apart. The other pair, R and GP, are very weakly linked. The effect is that Mendel was unlikely to have encountered genetic linkage. In any case, he did not report dihybrid experiments on either of these pairs, and only reported on the unlinked pairs, and he always found the ratio to be 9:3:3:1.[6]
| Seed shape | Round | Wrinkled | R | V | Yes | Starch branching enzyme 1 | 0.8-kb insertion | ||
| Stem length | Tall | Dwarf | LE | III | Yes | GA 3-oxidase1 | G-to-A substitution | ||
| Cotyledon color | Yellow | Green | I | I | Yes | Stay-green gene | 6-bp insertion | ||
| Seed coat/flower color | Purple | White | A | II | Yes | bHLH transcription factor | G-to-A at splice site | ||
| Pod color | Green | Yellow | GP | V | No | Chloroplast structure in pod wall | Unknown | ||
| Pod form | Inflated | Constricted | V | III | No | Sclerenchyma formation in pods | Unknown | ||
| Position of flowers | Axial | Terminal | FA | IV | No | Meristem function | Unknown |